1. Field of the Invention
The present invention relates generally to horizontal blinds, and specifically relates to blinds which prevent light passage when closed.
2. Description of the Prior Art
Horizontal or venetian blinds have existed for many years and have been used to cover windows, sliding glass doors and other openings to control the amount of light passing through the opening. They are made of a number of thin, horizontal wooden, metal, or plastic slats that can be set together at any angle to regulate the light and air passing through or be drawn up together to the top of the window by means of cords. The blinds serve functional, decorative, and privacy enhancing functions. A conventional blind system includes a head box which encloses the mechanism for adjusting the tilt of the slats and for raising and lowering the blind. Hanging down from the head box is a plurality of thin and relatively narrow slats which, depending on their length, are supported by at least two sets of ladder-like operating cords. Lifting cords connected to a lowermost slat or a bottom rail pass through each slat.
When the slats are tilted in a horizontal position, light passes through the blind. When the slats are tilted into a vertical position, the light is blocked. Since each slat is supported by a "rung" or horizontal cord attached to the set of operating cords, tilting the slats into the vertical position puts the horizontal cords between adjacent slats. This prevents the slats from fully closing. As a result, such prior art blind systems pass a certain amount of light. The presence of the lifting cords between the slats causes the separation of the closed slats to further increase, thereby increasing the amount of light which comes through the blind. Also, through holes for the lifting cords represent themselves an additional source of light leakage. That is, when the slats are tilted to the vertical position to block light, some light inevitably passes through the holes and slots in the blind. The overall effect of the holes and the presence of the horizontal cords between the slats when in the vertical position is that the blind does not fully block all of the light. This leads to a blind which is not as aesthetically pleasing as possible and has a reduced ability to provide privacy. In addition, light spots resulting from sunlight beams passing through the holes may in time leave fading spots on the walls and items hanging thereon.
Though venetian blinds have been used for several centuries and many attempts have been made to improve them, those numerous developments have not significantly changed this classic product other than on a refined scale such as narrow operating cords replacing wide ladder tapes, conversion to contemporary materials such as aluminum and plastics, and component improvements such as high-ratio gear wands replacing direct-drive tilt cords.
There appears to be at least two causes for the lack of solution to this light leakage problem. One is that venetian blinds have been the subject of continuous refinement over such a long time by so many contributors that they were believed to have evolved to their most efficient generic form.
The second cause is that in solving one problem the improvements either have inadvertently created another one or have compromised a prior accepted benefit to a level below consumer acceptance.
Illustrative of this dilemma is the problem of light leakage through blinds that has been addressed by many. U.S. Pat. No. 2,107,432 discloses a window covering made of pivoting louvers mounted at one pair of corners of the slat. When placed in the closed position, the louvers overlap one another. When the louvers are placed in the open position, they allow the most light to pass through the blind. The angle of the louvers is adjusted by a mechanical device causing the louvers to pivot. This design makes no provision for raising the louvers. Because the louvers cannot be raised, the window will always be partially covered by the blind.
There have been approaches to solve the light leakage problem by forcing the slats together when they are in the vertical position. U.S. Pat. No. 2,804,924 discloses a horizontal blind having a set of paired pivoting rods anchored to the top and bottom of the window casement. When it is desired to fully close the blind, the paired pivoting rods are actuated to clamp the slats together preventing the passage of light. To fully close the blind requires two actions; 1) tilting the slats to the vertical position, and 2) clamping the slats together with the pivoting rods. When the blind is raised, the rods remain in the window. The permanent presence of the rods is unsightly and prevents objects such as fans and air conditioning units from being placed in the full width of the window.
U.S. Pat. No. 5,409,050 teaches a window blind having pivotal slats which can be raised. There are two ladder holes in each slat which are located respectively near both ends of the long side of the slat and at a predetermined distance from a center line drawn along the longitudinal axis of the slat. Both ladder holes are corresponding in location to a first pair of operating cords and provided respectively with a slit extending in the same direction toward the edge of the same long side of the slat. Located by the ladder hole is a through hole for receiving a lifting cord. The first pair of the operating cords is received in the ladder holes through the slits. There is also a second pair of the operating cords which is so situated that its rung section supports the slat. As a result, an extension, unsupported section of the slat is formed. When the slats are so set as to keep out the light, the outer side edge of the extension section of an upper slat is lapped with the inner side edge of the extension section of a lower slat located immediately under the upper slat, thereby obstructing the through holes, concealing the operating cords and the lifting cord, and fully blocking the light. The slats may also be raised to allow full access to the window. Because the slat is supported only along its middle and along one edge, it is difficult to raise the free edge of the slats above the horizontal position. The angle of the slat cannot be adjusted to block light impinging on the blind from below. If the blind is used in an upper story window, or if the window is positioned near a body of water or snow, it is impossible to prevent others from looking into the room from below or to block the light reflected from below. Because the slat has a free edge wide enough to overlap the slat below, a blind of this design has a greater thickness than conventional blinds. Wider blinds protrude into the room and present an unattractive appearance.
U.S. Pat. No. 2,723,716 discloses a window blind slat having two sliding transverse portions arranged so that when the slat is rotated to a vertical position, adjacent slats overlap and cover the gap between adjacent slats and reduce the amount of light passing through the blind. Window blinds of this style are difficult and expensive to manufacture, subject to wear and unreliable in operation.
Efforts have also been made to eliminate the operating and lift cords from the interior of the blind slats. U.S. Pat. No. 5,375,642 discloses a horizontal blind having slats supported and operated by sets of attached flexible tilt members and raised by lift cords. The flexible tilt members have pins to support and operate the slats. The slats are counter-weighted to allow the lift members to operate the blind. When the slats are tilted, one set of flexible tilt members is raised relative to the other set. The counter-weighing feature assures that the slats will fully tilt. When the blind is raised, the flexible tilt members collapse allowing the blind to be raised without altering the angular position of the slats. All the merits of the structure notwithstanding, it is relatively complex and thus costly to manufacture.
One more patent addressing the problem is U.S. Pat. No. 5,423,367. A plurality of angle-shaped, or "V"-shaped slats are supported by ladder-shaped operating cords, which extend vertically from a bottom of a head box, and lifting cords, which extend from the head box through cord passage slots in the slats to a bottom rail of the blind. Each of the slats has a first, porous and semi-light-transmitting part extending from an apex portion of the slat to one side edge of the slat and a second, non-porous and non-light-transmitting part extending from the apex portion of the slat to another side edge of the slat. The structure provides a slight overlap of adjacent slats when the slats are fully tilted in one direction or the other. As a result, the lower edge of the upper slat slightly overlaps the upper corner of the lower slat, reducing the amount of light which passes between the slats. To exclude unwanted light, the cord passage slots formed in one surface of the slats extending to at least the apex of the "V" are used. When the slats are tilted into a position where the edges of the slats touch, each of the slots provides a recess for receiving the heavier lifting cord. Because of the non-planar "V" shape of the slats a significant portion of the blind blocks light when the slats are placed in the horizontal position such that when the blind is fully opened, a significant amount of transmitted light cannot pass through the opening. When conventional blinds are placed in the open position, the substantially flat slats allow more light to pass through the blind.